I'm playing an alea evangelii game with a friend of mine, and found an interesting edge case in the rules: I had fully surrounded him, but some of his pieces were at the edge of the board, so OpenTafl's surrounding-detection code did not rule it a victory. Play is ongoing, and it seems likely he'll succeed in building a draw fort in the center of the board, inside the cordon, without having to use the pieces trapped against the edge, so I won't be able to surround him according to OpenTafl's definition (that is, given as many moves as desired with no attacking responses allowed, no defending piece is able to reach an edge). The rule as stated there is correct for Copenhagen, where edges are important, but seems to me to be incorrect for Fetlar and alea evangelii.
Excepting Copenhagen, where play at the edges inside a cordon can determine the outcome of a game, I think I may change the surrounding victory rule in OpenTafl to read, 'given as many moves as desired with no attacking responses allowed, no defending piece is able to reach a victory space'. What are your thoughts?